The present invention relates in general to fiber optic detection systems, and more particularly to a fiber optic detection system employing a single fiber optic element.
The patent to McMahon, U.S. Pat. No. 4,689,484, issued on Aug. 25, 1987, for Photoelectric Leak Detection System For Double-Walled Tanks And The Like discloses a photoelectric leak detection system for a double-walled tank in which a pair of optical fibers extend from the top to the bottom of a double-walled tank within the space between the walls. At the lower ends of the optical fibers are respective probes. A light source is positioned at the upper end of one of the optical fibers and a photodiode is disposed at the upper end of the other optical fiber to detect changes in the reflected light conducted through the other optical fiber. The leak detector uses a transparent body at the terminal ends of the optical fibers and a spacer support for maintaining the terminal ends of the optical fibers and the transparent body above the bottom of the tank.
In the patent to Hansel et al., U.S. Pat. No. 4,069,838, granted on Jan. 24, 1978, for Fiber Optic Liquid Level Sensor, there is disclosed a liquid level sensor employing a single fiber optic tube. At one end of the fiber optic tube is a source of light. At the other end of the fiber optic tube is a light detection device. The fiber optic tube is interrupted to form a gap section with a pair of gaps. Light is cast onto liquid through one gap and refracted light passes through the other gap to be sensed by the light detection device. When the liquid in a container rises into the gap, the light passing through the fiber optic tube is interrupted.
In the patent to Robert C. Harding, U.S. Pat. No. 4,354,180, issued on Oct. 12, 1982, for Electro-Optical Liquid Level Sensor, there is disclosed a liquid level sensing device in which there is a light conductor and an electrical conductor. A source of light is located at the upper end of the light conductor and an electro-optical transducer is located at the lower end of the light conductor. One electro-optical transducer at the lower end of the light conductor casts a beam of light toward liquid through a transparent probe. The electro-optical transducer at the lower end of the light conductor is disposed in spaced relation to the probe. Another electro-optical transducer is disposed in spaced relation to the probe for receiving reflected light passing through the transparent probe. The other electro-optical transducer is connected to the electrical conductor. The beam of light is constantly reflected toward the light detecting transducer regardless of whether the probe is above the liquid or immersed in the liquid. The amplitude of the signal transmitted by the light detecting transmitter is greater when the probe is above the level of the liquid and is lesser when the probe is immersed in the liquid. The probe uses a transparent body having an index of refraction.
The patent to Neuscheler et al., U.S. Pat. No. 3,995,168, issued on Nov. 30, 1976, for Electro Optical Fluid Measurement System, discloses a device for the remote display of the level of a liquid and specific density of the liquid contained within a tank. The device includes a pair of fiber optic bundles. One fiber optic bundle conducts light from a source to be cast toward liquid in a tank. The other fiber optic bundle receives reflected light and conducts the reflected light to phototransistors. The terminal ends of the fiber optic bundles are held by a plate and form confronting faces at an angle of 45.degree.. A prism is disposed in the space formed by the confronting surfaces of the terminal ends of the fiber optic bundles. When light detected by the other fiber optic bundle is reflected by the level of liquid being below the prism, the phototransistors will produce a signal indicating the level of the liquid is below the prism.
In the patent to Spiteri, U.S. Pat. No. 4,155,013, issued on May 15, 1979, for a Liquid Level Indicator, there is disclosed a liquid level monitor having a pair of fiber optic cables. Light from a source of light is conducted through one of the fiber optic cables. The fiber optic cables terminate in a prism within a probe. The prism is immersed in oil. The absence of oil causes the light conducted through the one fiber optic cable to impinge on a face of the prism at an angle greater than a critical angle. Light is reflected through the prism and emitted from another face of the prism to be conducted through the other fiber optic cable. If the prism is above the oil level, the light is totally reflected for conduction through the other fiber optic cable. When the prism is immersed in oil, the light is not reflected by the prism surface.
The patent to Vaccari, U.S. Pat. No. 4,156,149, granted on May 22, 1979, for Optical Material Level Probe, discloses an optical level detection probe having spaced apart guides mounted on an epoxy support. Each guide has a 45.degree. angle reflecting face and the reflecting faces oppose one another. When material reaches the reflecting surfaces, the light is not transmitted from one guide to the other guide. When material is below the reflecting surfaces, light travels from one reflecting surface to the other reflecting surface to be detected by a light sensor.